1. FIELD OF THE INVENTION
The present invention relates to a vibrational angular velocity sensor used for detecting a travel direction of an automotive vehicle, for instance.
2. Description of the Prior Art
Conventionally, there exists a prior-art vibrational angular velocity sensor assembly 30 as shown in FIG. 1(A).
In the drawing, the numeral 31 denotes a vibrational angular velocity sensor which can output an electric signal according to a rotational force applied to the vibrating sensor. When a driving signal is applied to a piezoelectric element 31a, a vibrator 31b on which the piezoelectric element 31a is coated is vibrated with its support pins 31c as nodes. The numeral 32 denotes an upper casing lid; 33 denotes support plates; 34 denotes a casing. The upper casing lid 32, the support plates 33 and the casing 34 are made of a metal such as Ni-Cr alloy. The vibrational angular velocity sensor 31 is disposed within the casing 34, fixed by the support plates 33, and covered by the upper casing lid 32.
Although the prior-art vibrational angular velocity sensor is constructed as described above, since the vibrational angular velocity sensor is subjected to the influence of temperature or humidity, there exists a problem in that the output selectivity drifts according to change in temperature and/or humidity. Therefore, the sensor is usually installed within a constant temperature tank.
However, when a constant temperature tank is used, there exists a problem in that the size of the assembly is large; the structure is complicated; and the influence of viscous resistance due to air within the constant temperature tank is not negligible.
Further, to evacuate a casing 34 into a high vacuum, getter is usually placed within the casing 34 and burnt away to heighten the degree of vacuum. However, when the getter is simply placed within the casing and then burnt, there exists a problem in that the angular velocity vibrator 31b is heated and therefore the characteristics thereof are deteriorated. In addition, there exists another problem in that when a getter is placed within the casing 34, the size of the casing increases.
Further, in the prior-art angular velocity sensor, when the casing 34 is made of metal, there exists a problem in that the vibrator housed within the casing is subjected to the influence of external radiant heat.
On the other hand, FIG. 1(B) shows a prior-art vibrational angular velocity sensor assembly 30 connected to a detection signal processing circuit 40. In the drawing, a vibrational angular velocity sensor assembly 30 is connected to a printed circuit board 40 on which a circuit is formed to process detection signals outputted from the vibrational angular velocity sensor 31 in a support casing 50 for fixing the vibrational angular velocity sensor assembly 30 and the printed circuit board 40 together. Further, the vibrational angular velocity sensor assembly 30 and the printed circuit board 40 are connected to each other by conductive wires (not shown).
In the prior-art vibrational angular velocity sensor assembly 30 connected to the circuit board 40, since the signal wires of the sensor are led out by conductive wires, it has been necessary to mechanically fix the vibrational angular velocity sensor assembly 30 and the signal processing circuit board 40 to the support casing 50 separately before connecting both electrically. Therefore, there exist problems in that the number of parts increases and it takes much wiring time or assembly time. Further, since relatively long conductive wires are used, there exists a problem in that the sensor is subjected to the influence of external noise.
Further, with reference to FIG. 1(A), since the casing 34 is made of metal in the prior-.art vibrational angular velocity sensor, external heat is readily conducted to the element inside the casing. Therefore, external temperature changes are readily transmitted through the support pin 31c to the vibrator 31b when an end of the support pin 31c for supporting the vibrator 31b is in contact with an outer air at the edge of the casing 34.